1. Field of the Invention
The invention relates to a process for preparing alkyl dihaloacetoacetates of the formula (I) by reacting α,α-dihaloamines of the formula (III) with carboxylic esters of the formula (II) in the presence of bases.
2. Description of Related Art
Alkyl difluoroacetoacetates are important synthesis units for preparing active agrochemical ingredients, especially for preparing pyrazolylcarboxanilides.
Tetrahedron 2001, 57, 2689-2700 discloses that 4,4-difluoroacetoacetic esters can be obtained by reacting ethyl difluoroacetoacetate with ethyl acetate in the presence of sodium hydride (NaH). The yield of this reaction is very unsatisfactory at 25%. Moreover, Tetrahedron 1996, 52, 119-130 states that 4,4-difluoroacetoacetic esters can be prepared by reacting ethyl difluoroacetate with ethyl bromoacetate in the presence of Zn.
WO-A-2005/003077 teaches a three-stage process for preparing alkyl difluoroacetoacetates proceeding from chlorodifluoroacetoacetic esters by reducing the chlorine atom with trialkoxyphosphines (P(OAlk)3), which is also known as the Perkow reaction.
WO-A-2006/005612 teaches a process for preparing 4,4-difluoro-3-oxobutyric esters by reacting 2,2-difluoro-N,N-dialkylacetamide with acetic esters in the presence of bases. The alkyl 4,4-difluoro-3-oxobutyrate is subsequently, as described in JACS, 73, 3684 (1951), reacted with trimethyl orthoformate and acetic anhydride to give ethyl (2-ethoxymethylene)-4,4-difluoromethylacetoacetate which, according to U.S. Pat. No. 5,489,624, can be converted using methylhydrazine to ethyl 3-difluoromethyl-1-methyl-4-pyrazolecarboxylate. The route described firstly includes a multitude of reaction steps, and the 2,2-difluoro-N,N-dialkylacetamide used is secondly not commercially available and can be obtained only in small yields of approx. 70% by fluorinating 2,2-dichloro-N,N-dialkylacetamide.
The processes described before in the prior art have the disadvantage that the difluorocarbonyl halides, haloalkylcarboxylic anhydrides and haloacrylic esters used are expensive, cause corrosion problems and/or can be purified only with a high level of technical complexity.